1. Field of the Invention
The invention relates to a magnetic resonance imaging apparatus, and particularly to a multipurpose dedicated imaging apparatus having improved features for imaging the region of the vertebral column under different load conditions.
2. Description of the Related Art
Imaging the vertebral column may require the possibility of bringing the patient in an upright position in order to have the vertebral column loaded by the weight of the patient. In the normal laying down position of the patient on a bed or table having an horizontal orientation, the vertebral column will be in an unloaded and ideal condition. Thus, most pathologies may not arise clearly and the examination will lead to unclear results or to negative results despite the fact that the patient is showing typical symptoms of a disease of the vertebral column.
Most spinal disease can be best evaluated by imaging the anatomic region with the patient having different postures particularly a posture in which the patient is bent as a sitting position or a forward leaned position. Furthermore for best imaging the anatomic region it might be advantageous to be able to take images of the spine according to differently oriented imaging planes corresponding to different orientation of the static field direction parallel to a front/rear section plane of the patient or to a lateral section plane of the patient. The possibility of assuming different positions within the poles of a MRI apparatus are also important when interventions has to be carried out during the imaging process. In this case the patient position relative to the magnetic structure is important for leaving enough free space for the medical personal to reach the anatomic region where the intervention has to be carried out.
Allowing that the patient can assume different postures is also very important, since in case of pathological conditions the patient cannot take some postures for a long time without suffering pain. Since imaging sequences need normally a long time to be carried out in a manner of furnishing images of the anatomic region which are useful for diagnostic purposes, the patient must be able to maintain a certain position without making any movement for such a long time, which is impossible or at least highly disagreeable when the said position is associated with a posture of the patient at which the patient experiences pain.
Furthermore it is also relevant to ensure the possibility of carrying out a range as wide as possible of imaging different anatomical districts with one and the same imaging apparatus.
Actually known magnetic resonance imaging apparati use so called total body scanners which magnetic structure houses the entire body or a considerable part of it inside the patient examining space defined by the magnetic structure.
U.S. Pat. No. 6,414,490 and U.S. Pat. No. 6,504,371 disclose magnetic resonance imaging apparatus of the above mentioned kind. The magnetic structure is designed to generate a horizontal magnetic field. The patient is brought inside the examining space by means of a patient positioning device which is a bed or table mounted on a carriage, which bed or table can be further tilted around horizontal axis for giving different orientations to the bed or table with respect to the vertical direction. Furthermore, in order to focus the region of the patient to be imaged, the bed or table or carriage may be associated with an elevator which displaces the patient up and down relative to the examining space between the poles of the magnetic structure.
The patient positioning device is also relative expensive due to the fact that the tiltable or swingable bed or table and the elevator for displacing the patient relative to the imaging space in the magnetic structure are mounted on a carriage.
On the other hand, even if the anatomic region of the vertebral column is a very large one, usually examination through imaging is carried out for only a certain specific part of the vertebral column.
U.S. Pat. Nos. 5,689,190 and 5,666,056 disclose an MRI apparatus in which the poles of the magnetic structure have opposite surfaces delimiting an imaging space which surfaces are parallel to one another and which surfaces are oriented at an angle relative to a bed or table where the patient is laying. The bed or the table can be displaced along two perpendicular axes which are parallel to the plane defined by them.
Also in this case the magnetic structure is very big and there is a need of different patient supporting devices in order of allowing the patient to take different positions such as a laying position and a sitting position.
U.S. Pat. No. 6,011,396 shows a displaceable MRI apparatus which is mounted on a carriage and which has a magnetic structure with two opposite poles having surfaces limiting an image volume which are parallel one with respect to the other and oriented vertically. The two poles are tiltable together along the said vertical planes and have a relative distance which allow to drive between the two poles different devices for supporting a patient such as a table, a bed or a seat.
This MRI apparatus is indeed very small. Nevertheless for imaging the patient in different positions, particularly in a upright position, an elevator for the relative heavy magnetic structure is needed which on the other hand will have a correspondingly strong construction. Since the patient supporting and/or retaining device is a normal device such as a bed a seat or the like, no particular device is provided which is mechanically linked to the magnetic structure in order of having a precise and controlled relative positioning of the patient and of the magnetic structure.
U.S. Pat. No. 5,423,315 discloses an MRI apparatus having a thin annular magnetic structure which is mounted on a supporting frame allowing the said annular magnetic structure to be tilted around a first diametric axis and a second axis coinciding with the central axis of the annular magnetic structure. Furthermore the annular structure can be displaced along a vertical axis.
In the case of this device, the annular magnetic structure must have a very large diameter in order to allow access of the medical personal to the anatomical region of patient which is subjected to imaging.
Most of the actual devices are very big, heavy, and expensive. Big and heavy magnetic structures have problems of installation, since the room where the imaging apparatus has to be installed must necessarily have a floor which can support the weight of the imaging apparatus. Furthermore, the room must be sufficiently big to permit installation.